Liquid helium at a temperature of 4.2.degree. K. is usually used as a cooling agent in electrical machines with cryogenic cooling. The coolant feed unit, which is used for supplying the liquid coolant from a stationary tank to the rotary superconducting field winding of the electrical machine, is an important component of such a machine. A distinctive feature of liquid helium supply is the appearance of a two-phase flow due to evaporation of a portion of helium caused by the frictional of the flow of liquid helium about the rotating parts of the electrical machine and the local hydraulic losses of the helium flow.
The quantitative proportion of the liquid and gas phases of the coolant, i.e. the efficiency of the cooling of the superconducting field winding determining the output power and efficiency of the entire electrical machine, depends on the design and operating conditions (flow rate, pressure, temperature of the cooling agent) of the cooling agent feed unit. An insufficiently effective cooling film can cause boiling conditions to be established in the cooling channels of the superconducting field winding, and this results in a loss of superconducting properties of the superconductor.
Known in the art is a device for checking the condition of the coolant at the output of a coolant circuit of an electrical machine with cryogenic cooling (cf. P.A.Rios, B.B.Gamble and E.T.Lascaris. Development of a Coolant Circuit for Rotors of Superconducting generators. Conference on Technical Application of Superconductivity. Alushta, USSR, September 16-19, General Electric) having a stationary part made of two coaxial tubes arranged with a gap with respect to each other and a movable part comprising a hollow rotor, in which a cryogenic temperature is maintained and having at one end, coaxially with the hollow rotor, a coolant feed unit of the machine whose stationary portion communicates through one end with a coolant feed tank, while the movable portion communicates with a coolant collecting chamber and a coolant removing unit for feeding the coolant into the coolant receiver tank, said chamber and unit being arranged inside the hollow rotor.
This device is a model of an electrical machine with cryogenic cooling and it comprises all basic elements of such an electrical machine, therefore, it features a complex design. The coolant removing unit also has a complex design. The coolant is removed from the chamber for collecting the coolant through passages disposed in the shell and bottoms of these chambers, in a thermal shield, inside the shaft. The coolant condition in the collecting chamber is monitored by the level of the liquid phase of the coolant, and this requires the use of a current-collecting member in the model, which complicates its construction, because one end of the rotor is coupled to a drive and the other end carries a coolant feed unit and has passages for removing the coolant from the coolant collecting chamber.
The basic object of the invention is to provide a device for checking the condition of the coolant at the output of the coolant feed unit of an electrical machine with cryogenic cooling whose design makes it possible to simplify the measurement of the proportion of the liquid and gaseous phases of the coolant at the feed unit output.